348 



RICHARD E. SCAMMON 



and the preceding stage show a shght but distinct rotation of 

 the anterior part of the Hver to the left around the fore gut as an 

 axis. 



A considerable advance in development is seen in an embryo 

 only a millimeter longer than the preceding one. This specimen 

 corresponds fairly well with Balfour's stage I, or No. 24 of the 

 Normal plate series the embryos of which measured 11.5 mm. 

 It has sixty-five segments, three open gill slits and two unopened 

 gill pouches and four turns of the spiral valve. A reconstruction 

 of the liver and adjoining archenteron is illustrated in figures 28, 



Vomi 



gl latlupp 



Fig. 8 Three transverse .sections through the liver region of an Acanthias 

 embryo 10mm. long (S.C. 20). X 50. A, Through the anterior partof themedian 

 hepatic pouch (pars hepatica mediana). B, Through the posterior part of the 

 median pouch (pars ductus mediana). C, Through the gut just posterior to the 

 liver proper showing the pars ductus lateralis. F.g., fore gut; G.bl., gall bladder; 

 Lat.hep.p., lateral hepatic pouch; P-arch.g., para-archenteric groove; P.duct.lat., 

 pars ductus lateralis; P., pars hepatica mediana; V.omph.L, V.omph.r.. loft and 

 right omphalo-mesentcric veins; .Y, anlage of the ductus cholodochus. 



39 and 40. The process by which the hepatic pouch will even- 

 tually be separated from the gut above is well under way. The 

 median hepatic pouch from which the lateral pouches spring and 

 to which the lateral pouches are attached is rather triangular in 

 cross section anterior to the origin of the lateral pouches. The 

 broader part is below and the narrow dorsal extremity joins the 

 floor of the fore gut anteriorly a little to the right of the median 

 Hne (fig. 8 ^). 



The ventral part of the gut is also rotated to the right so that 

 these two structures join at an oblique angle thus forming a broad 



